Lipids

In this lesson, you're going to learn about the different types of lipids, their structure and function your body. Specifically you will look at the following:

1. Lipid Characteristics Overview
2. Fats
3. Triglycerides
4. Phospholipids
5. Sterols

1. Lipid Characteristics Overview

Lipids are molecules that are nonpolar. They contain hydrogen, carbon, and oxygen. They are an organic molecule, and they don't dissolve in water, which ties with them being nonpolar.

Lipid

An organic molecule made up of glycerol and fatty acids, which is non-polar and does not dissolve easily in water

Nonpolar

Does not dissolve easily in water

2. Fats

So fats are a type of lipid that have a fatty acid tail attached to a glycerol molecule.

Fat

A lipid made of a glycerol molecule and a fatty acid side chain

Each of those fatty acid tails contains up to 36 carbons as the backbone of the fatty acid, and also contains a carboxyl group at one end. Most of the bonding space that's available in the fatty acid tail is occupied by hydrogens.

There are two main categories of fats.

1. Saturated fats

Saturated fats are a type of fats that only contain single covalent bonds in the fatty acid tail.

Saturated Fat

A type of fat which does not have double bonds in its side chain

Oftentimes saturated fats are animal fats and they're generally solid at room temperature, because they're more tightly packed together.

An example of a saturated fat would be lard.

2. Unsaturated fats

Unsaturated fat is a type of fat that has one or more double covalent bonds between carbons, which are the backbone of the fatty acid.

Unsaturated Fat

A type of fat which has double bonds in its side chain

An example of an unsaturated fat might be vegetable oil or olive oil.

Generally unsaturated fats are more plant-based, where saturated fats are more animal-based. So they're less tightly packed, and they're usually liquid at room temperature.

Think of olive oil as an example. You know that's liquid at room temperature, because they're less tightly packed.

Generally unsaturated fats are a little bit healthier than saturated fats, but there are some unsaturated fats, such as trans fats, that are more unhealthy.

Trans Fat

A type of unsaturated fat which is unhealthy and may lead to health problems

So you’re going to take a look here at what saturated fats vs unsaturated fats might look like. See the glycerol molecule below.

The fatty acid tail is attached to a glycerol molecule. So you have your glycerol molecule on the top, and then your fatty acid tail connected to that. The fatty acid tail is made of a carbon backbone, and it can have up to 36 of those. It's going to vary depending on the type of fat that it is. So you have the carbon bonded to hydrogens.

You'll notice that they are all single covalent bonds. There aren’t any double bonds between hydrogens in this example. You'll notice they're all single bonds between the carbons, and then most of the bonding space here is occupied by hydrogens. So that would be an example of a saturated fat.

Now see the unsaturated fat image below.

Unsaturated fats have one or more double covalent bonds between the carbons within your carbon backbone. But in an unsaturated fat, you might have a double bond. So you'll notice the double bond between the carbons would make this an unsaturated fat.

In unsaturated fats, because of the double bonds, the fatty acid tail is usually kinked, which, again, allows them to be packed less tightly, making them generally liquid at room temperature.

Another type of unsaturated fat you could have something called a polyunsaturated fat. So the prefix "poly" means many. It means that it's going to have not just one double bond, but it could have many double bonds.

3. Triglycerides

Triglycerides look similar in structure to fats, but the prefix "tri" means three, so rather than just having one fatty acid tail, it has three.Triglycerides are the most common lipid in your body, and they contain lots of energy. An example of a triglyceride might be butter, or lard, oils.

Triglyceride

A type of lipid which is made up of a glycerol molecule and three fatty acid side chains

4. Phospholipids

Phospholipids are a type of lipid that are found in the cell membrane of the cells in your body. Phospholipids are made up of a hydrophilic head, and they're made up of two hydrophobic tails.

Phospholipid

A type of lipid made up of a hydrophilic head and hydrophobic tail, and is found in cell membranes

Something that is hydrophilic is attracted to water, whereas something that is hydrophobic is repelled by water. So in the structure of your cell membranes, the phospholipids are arranged in a bilayer.

See the drawing of a phospholipid below.

The head faces out and all of the tails face in. The heads are hydrophilic, meaning they're attracted to water. So those heads are pointed to the outside-- or to the inside of the cell-- where there's water. Whereas the hydrophobic tails are pointed inward, away from water.

5. Sterols

Sterols are lipids that don't have a fatty acid tail so their structure is a little bit different.

Sterol

A type of lipid containing only a glycerol molecule

Some common examples of sterols would be cholesterol in your body. It's a lipid that doesn't have a fatty acid tail and steroid hormones, like estrogen and testosterone, are examples of sterols.

So this lesson has been an overview of the different types of lipids, the structure and function of them in your body. In this lesson you learned that lipids are nonpolar, don't dissolve in water, and they're organic molecules containing hydrogen, carbon, and oxygen. You also went in-depth and learned more about fats, triglycerides, phospholipids, and sterols.

Keep up the learning and have a great day!